How to Achieve Nanoscale Imaging of Milliscale Features – AFM Profiler Mode

Table of Contents

Introduction
Analyzing the Depth and Surface Roughness of a Surface Crater with the VLS-80

Introduction

Obtaining nanometer resolution in roughness and depth measurements can be a challenging feat when analyzing craters that are several millimeters wide.

This is not the case with the VLS-80 the novel profiler-mode AFM enables profiling of features of several millimeters with nanometer resolution either in contact or in dynamic mode. This article discusses a profiler experiment conducted to analyze a surface crater.

The one-dimensional profile provides clear information on the depth of the crater and a first overview of the roughness. Accurate roughness analysis measured by AFM imaging can subsequently be performed by clicking on any position on the profile, using it as a guide. This is called zoom-to-AFM.

Analyzing the Depth and Surface Roughness of a Surface Crater with the VLS-80

The combination of AFM and long-distance profiling offers a reliable and accurate analysis of the crater, whether in air or in high-vacuum.

Figure 1 shows a snapshot taken with the top-view camera of the VLS-80. The Auger crater, which is more than 1 mm in diameter is easily recognizable. It has been placed below the cantilever using the motorized sample stage.

The red spot is the laser light reflected on the back of the cantilever. The one-dimensional profile was taken along the dotted line in just 3 minutes.

Figure 1. Top-view camera image showing the surface crater. The AFM cantilever can be seen in the centre of the image extending half way up the image. The dotted line indicates where the profile was taken

The profile displayed in Figure 2 shows that the crater has no real depth with respect to the rim but instead exhibits a variable roughness across its span. What at first glance may look like noise are actually features at the nanoscale represented over more than a millimetre.

Figure 2. Trace of the crater’s initial one-dimensional scan. Note: the y scale is in nm while the x scale is in µm. Sample courtesy of Dr. S. Facsko, HZDR, Germany.

As Figure 3 attests, a zoom into a one-micron long portion of the profile (at position A) reveals that the signal measured is topography with nanometer features and not noise. These features could not have been measured with a standard stylus profilometer as the lateral resolution of such an instrument is too poor.

Figure 3. This zoom shows forward and backward traces overlapping: it proves that spikes are topography, not noise.

With just a few clicks, the tip can then be moved to the area of interest and an AFM image can be captured either in contact or in dynamic mode. Figure 4 shows a series of four AFM images taken in contact mode measured at four different positions of the profile (positions are marked on Figure 1). The images reveal different surface topography and hence different roughness.

Figure 4. AFM images taken from four distinct areas of the profile.

It is worth noting is that the VLS-80 is compatible with the sample holders of the TOF.SIMS 5 from ION-TOF. The software handshake makes it quick and easy to relocate it to a SIMS measurement area.

This information has been sourced, reviewed and adapted from materials provided by NanoScan AG.

For more information on this source, please visit NanoScan AG.

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